CONFIGURATION.md

Configuration

Telegraf's configuration file is written using TOML and is composed of three sections: global tags, agent settings, and plugins.

Generating a Configuration File

A default config file can be generated by telegraf:

telegraf config > telegraf.conf

To generate a file with specific inputs and outputs, you can use the --input-filter and --output-filter flags:

telegraf config --input-filter cpu:mem:net:swap --output-filter influxdb:kafka

View the full list of Telegraf commands and flags or by running telegraf --help.

Windows PowerShell v5 Encoding

In PowerShell 5, the default encoding is UTF-16LE and not UTF-8. Telegraf expects a valid UTF-8 file. This is not an issue with PowerShell 6 or newer, as well as the Command Prompt or with using the Git Bash shell.

As such, users will need to specify the output encoding when generating a full configuration file:

telegraf.exe config | Out-File -Encoding utf8 telegraf.conf

This will generate a UTF-8 encoded file with a BOM. However, Telegraf can handle the leading BOM.

Configuration Loading

The location of the configuration file can be set via the --config command line flag.

When the --config-directory command line flag is used files ending with .conf in the specified directory will also be included in the Telegraf configuration.

On most systems, the default locations are /etc/telegraf/telegraf.conf for the main configuration file and /etc/telegraf/telegraf.d for the directory of configuration files.

Environment Variables

Environment variables can be used anywhere in the config file, simply surround them with ${}. Replacement occurs before file parsing. For strings the variable must be within quotes, e.g., "${STR_VAR}", for numbers and booleans they should be unquoted, e.g., ${INT_VAR}, ${BOOL_VAR}.

Users need to keep in mind that when using double quotes the user needs to escape any backslashes (e.g. "C:\\Program Files") or other special characters. If using an environment variable with a single backslash, then enclose the variable in single quotes which signifies a string literal (e.g. 'C:\Program Files').

In addition to this, Telegraf also supports Shell parameter expansion for environment variables which allows syntax such as:

• ${VARIABLE:-default} evaluates to default if VARIABLE is unset or empty in the environment.
• ${VARIABLE-default} evaluates to default only if VARIABLE is unset in the environment. Similarly, the following syntax allows you to specify mandatory variables:
• ${VARIABLE:?err} exits with an error message containing err if VARIABLE is unset or empty in the environment.
• ${VARIABLE?err} exits with an error message containing err if VARIABLE is unset in the environment.

When using the .deb or .rpm packages, you can define environment variables in the /etc/default/telegraf file.

Example:

/etc/default/telegraf:

For InfluxDB 1.x:

USER="alice"
INFLUX_URL="http://localhost:8086"
INFLUX_SKIP_DATABASE_CREATION="true"
INFLUX_PASSWORD="monkey123"

For InfluxDB OSS 2:

INFLUX_HOST="http://localhost:8086" # used to be 9999
INFLUX_TOKEN="replace_with_your_token"
INFLUX_ORG="your_username"
INFLUX_BUCKET="replace_with_your_bucket_name"

For InfluxDB Cloud 2:

# For AWS West (Oregon)
INFLUX_HOST="https://us-west-2-1.aws.cloud2.influxdata.com"
# Other Cloud URLs at https://v2.docs.influxdata.com/v2.0/reference/urls/#influxdb-cloud-urls
INFLUX_TOKEN=”replace_with_your_token”
INFLUX_ORG="yourname@yourcompany.com"
INFLUX_BUCKET="replace_with_your_bucket_name"

/etc/telegraf.conf:

[global_tags]
  user = "${USER}"

[[inputs.mem]]

# For InfluxDB 1.x:
[[outputs.influxdb]]
  urls = ["${INFLUX_URL}"]
  skip_database_creation = ${INFLUX_SKIP_DATABASE_CREATION}
  password = "${INFLUX_PASSWORD}"

# For InfluxDB OSS 2:
[[outputs.influxdb_v2]]
  urls = ["${INFLUX_HOST}"]
  token = "${INFLUX_TOKEN}"
  organization = "${INFLUX_ORG}"
  bucket = "${INFLUX_BUCKET}"

# For InfluxDB Cloud 2:
[[outputs.influxdb_v2]]
  urls = ["${INFLUX_HOST}"]
  token = "${INFLUX_TOKEN}"
  organization = "${INFLUX_ORG}"
  bucket = "${INFLUX_BUCKET}"

The above files will produce the following effective configuration file to be parsed:

[global_tags]
  user = "alice"

[[inputs.mem]]

# For InfluxDB 1.x:
[[outputs.influxdb]]
  urls = "http://localhost:8086"
  skip_database_creation = true
  password = "monkey123"

# For InfluxDB OSS 2:
[[outputs.influxdb_v2]]
  urls = ["http://127.0.0.1:8086"] # double check the port. could be 9999 if using OSS Beta
  token = "replace_with_your_token"
  organization = "your_username"
  bucket = "replace_with_your_bucket_name"

# For InfluxDB Cloud 2:
[[outputs.influxdb_v2]]
  # For AWS West (Oregon)
  INFLUX_HOST="https://us-west-2-1.aws.cloud2.influxdata.com"
  # Other Cloud URLs at https://v2.docs.influxdata.com/v2.0/reference/urls/#influxdb-cloud-urls
  token = "replace_with_your_token"
  organization = "yourname@yourcompany.com"
  bucket = "replace_with_your_bucket_name"

Secret-store secrets

Additional or instead of environment variables, you can use secret-stores to fill in credentials or similar. To do so, you need to configure one or more secret-store plugin(s) and then reference the secret in your plugin configurations. A reference to a secret is specified in form @{<secret store id>:<secret name>}, where the secret store id is the unique ID you defined for your secret-store and secret name is the name of the secret to use. NOTE: Both, the secret store id as well as the secret name can only consist of letters (both upper- and lowercase), numbers and underscores.

Example:

This example illustrates the use of secret-store(s) in plugins

[global_tags]
  user = "alice"

[[secretstores.os]]
  id = "local_secrets"

[[secretstores.jose]]
  id = "cloud_secrets"
  path = "/etc/telegraf/secrets"
  # Optional reference to another secret store to unlock this one.
  password = "@{local_secrets:cloud_store_passwd}"

[[inputs.http]]
  urls = ["http://server.company.org/metrics"]
  username = "@{local_secrets:company_server_http_metric_user}"
  password = "@{local_secrets:company_server_http_metric_pass}"

[[outputs.influxdb_v2]]
  urls = ["https://us-west-2-1.aws.cloud2.influxdata.com"]
  token = "@{cloud_secrets:influxdb_token}"
  organization = "yourname@yourcompany.com"
  bucket = "replace_with_your_bucket_name"

Notes

When using plugins supporting secrets, Telegraf locks the memory pages containing the secrets. Therefore, the locked memory limit has to be set to a suitable value. Telegraf will check the limit and the number of used secrets at startup and will warn if your limit is too low. In this case, please increase the limit via ulimit -l.

If you are running Telegraf in an jail you might need to allow locked pages in that jail by setting allow.mlock = 1; in your config.

Intervals

Intervals are durations of time and can be specified for supporting settings by combining an integer value and time unit as a string value. Valid time units are ns, us (or µs), ms, s, m, h.

[agent]
  interval = "10s"

Global Tags

Global tags can be specified in the [global_tags] table in key="value" format. All metrics that are gathered will be tagged with the tags specified. Global tags are overridden by tags set by plugins.

[global_tags]
  dc = "us-east-1"

Agent

The agent table configures Telegraf and the defaults used across all plugins.

• interval: Default data collection interval for all inputs.

• round_interval: Rounds collection interval to interval ie, if interval="10s" then always collect on :00, :10, :20, etc.

• metric_batch_size: Telegraf will send metrics to outputs in batches of at most metric_batch_size metrics. This controls the size of writes that Telegraf sends to output plugins.

• metric_buffer_limit: Maximum number of unwritten metrics per output. Increasing this value allows for longer periods of output downtime without dropping metrics at the cost of higher maximum memory usage.

• collection_jitter: Collection jitter is used to jitter the collection by a random interval. Each plugin will sleep for a random time within jitter before collecting. This can be used to avoid many plugins querying things like sysfs at the same time, which can have a measurable effect on the system.

• collection_offset: Collection offset is used to shift the collection by the given interval. This can be be used to avoid many plugins querying constraint devices at the same time by manually scheduling them in time.

• flush_interval: Default flushing interval for all outputs. Maximum flush_interval will be flush_interval + flush_jitter.

• flush_jitter: Default flush jitter for all outputs. This jitters the flush interval by a random amount. This is primarily to avoid large write spikes for users running a large number of telegraf instances. ie, a jitter of 5s and interval 10s means flushes will happen every 10-15s.

• precision: Collected metrics are rounded to the precision specified as an interval.

  Precision will NOT be used for service inputs. It is up to each individual service input to set the timestamp at the appropriate precision.

• debug: Log at debug level.

• quiet: Log only error level messages.

• logtarget: Log target controls the destination for logs and can be one of "file", "stderr" or, on Windows, "eventlog". When set to "file", the output file is determined by the "logfile" setting.

• logfile: Name of the file to be logged to when using the "file" logtarget. If set to the empty string then logs are written to stderr.

• logfile_rotation_interval: The logfile will be rotated after the time interval specified. When set to 0 no time based rotation is performed.

• logfile_rotation_max_size: The logfile will be rotated when it becomes larger than the specified size. When set to 0 no size based rotation is performed.

• logfile_rotation_max_archives: Maximum number of rotated archives to keep, any older logs are deleted. If set to -1, no archives are removed.

• log_with_timezone: Pick a timezone to use when logging or type 'local' for local time. Example: 'America/Chicago'. See this page for options/formats.

• hostname: Override default hostname, if empty use os.Hostname()

• omit_hostname: If set to true, do no set the "host" tag in the telegraf agent.

• snmp_translator: Method of translating SNMP objects. Can be "netsnmp" (deprecated) which translates by calling external programs snmptranslate and snmptable, or "gosmi" which translates using the built-in gosmi library.

• statefile: Name of the file to load the states of plugins from and store the states to. If uncommented and not empty, this file will be used to save the state of stateful plugins on termination of Telegraf. If the file exists on start, the state in the file will be restored for the plugins.

• always_include_local_tags: Ensure tags explicitly defined in a plugin will always pass tag-filtering via taginclude or tagexclude. This removes the need to specify local tags twice.

• always_include_global_tags: Ensure tags explicitly defined in the global_tags section will always pass tag-filtering via taginclude or tagexclude. This removes the need to specify those tags twice.

• skip_processors_after_aggregators: By default, processors are run a second time after aggregators. Changing this setting to true will skip the second run of processors.

Plugins

Telegraf plugins are divided into 4 types: inputs, outputs, processors, and aggregators.

Unlike the global_tags and agent tables, any plugin can be defined multiple times and each instance will run independently. This allows you to have plugins defined with differing configurations as needed within a single Telegraf process.

Each plugin has a unique set of configuration options, reference the sample configuration for details. Additionally, several options are available on any plugin depending on its type.

Input Plugins

Input plugins gather and create metrics. They support both polling and event driven operation.

Parameters that can be used with any input plugin:

• alias: Name an instance of a plugin.

• interval: Overrides the interval setting of the agent for the plugin. How often to gather this metric. Normal plugins use a single global interval, but if one particular input should be run less or more often, you can configure that here.

• precision: Overrides the precision setting of the agent for the plugin. Collected metrics are rounded to the precision specified as an interval.

  When this value is set on a service input, multiple events occurring at the same timestamp may be merged by the output database.

• collection_jitter: Overrides the collection_jitter setting of the agent for the plugin. Collection jitter is used to jitter the collection by a random interval. The value must be non-zero to override the agent setting.

• collection_offset: Overrides the collection_offset setting of the agent for the plugin. Collection offset is used to shift the collection by the given interval. The value must be non-zero to override the agent setting.

• name_override: Override the base name of the measurement. (Default is the name of the input).

• name_prefix: Specifies a prefix to attach to the measurement name.

• name_suffix: Specifies a suffix to attach to the measurement name.

• tags: A map of tags to apply to a specific input's measurements.

The metric filtering parameters can be used to limit what metrics are emitted from the input plugin.

Examples

Use the name_suffix parameter to emit measurements with the name cpu_total:

[[inputs.cpu]]
  name_suffix = "_total"
  percpu = false
  totalcpu = true

Use the name_override parameter to emit measurements with the name foobar:

[[inputs.cpu]]
  name_override = "foobar"
  percpu = false
  totalcpu = true

Emit measurements with two additional tags: tag1=foo and tag2=bar

NOTE: With TOML, order matters. Parameters belong to the last defined table header, place [inputs.cpu.tags] table at the end of the plugin definition.

[[inputs.cpu]]
  percpu = false
  totalcpu = true
  [inputs.cpu.tags]
    tag1 = "foo"
    tag2 = "bar"

Alternatively, when using the inline table syntax, the tags do not need to go at the end:

[[inputs.cpu]]
  tags = {tag1 = "foo", tag2 = "bar"}
  percpu = false
  totalcpu = true

Utilize name_override, name_prefix, or name_suffix config options to avoid measurement collisions when defining multiple plugins:

[[inputs.cpu]]
  percpu = false
  totalcpu = true

[[inputs.cpu]]
  percpu = true
  totalcpu = false
  name_override = "percpu_usage"
  fieldexclude = ["cpu_time*"]

Output Plugins

Output plugins write metrics to a location. Outputs commonly write to databases, network services, and messaging systems.

Parameters that can be used with any output plugin:

• alias: Name an instance of a plugin.
• flush_interval: The maximum time between flushes. Use this setting to override the agent flush_interval on a per plugin basis.
• flush_jitter: The amount of time to jitter the flush interval. Use this setting to override the agent flush_jitter on a per plugin basis. The value must be non-zero to override the agent setting.
• metric_batch_size: The maximum number of metrics to send at once. Use this setting to override the agent metric_batch_size on a per plugin basis.
• metric_buffer_limit: The maximum number of unsent metrics to buffer. Use this setting to override the agent metric_buffer_limit on a per plugin basis.
• name_override: Override the original name of the measurement.
• name_prefix: Specifies a prefix to attach to the measurement name.
• name_suffix: Specifies a suffix to attach to the measurement name.

The metric filtering parameters can be used to limit what metrics are emitted from the output plugin.

Examples

Override flush parameters for a single output:

[agent]
  flush_interval = "10s"
  flush_jitter = "5s"
  metric_batch_size = 1000

[[outputs.influxdb]]
  urls = [ "http://example.org:8086" ]
  database = "telegraf"

[[outputs.file]]
  files = [ "stdout" ]
  flush_interval = "1s"
  flush_jitter = "1s"
  metric_batch_size = 10

Processor Plugins

Processor plugins perform processing tasks on metrics and are commonly used to rename or apply transformations to metrics. Processors are applied after the input plugins and before any aggregator plugins.

Parameters that can be used with any processor plugin:

• alias: Name an instance of a plugin.
• order: The order in which the processor(s) are executed. starting with 1. If this is not specified then processor execution order will be the order in the config. Processors without "order" will take precedence over those with a defined order.

The metric filtering parameters can be used to limit what metrics are handled by the processor. Excluded metrics are passed downstream to the next processor.

Examples

If the order processors are applied matters you must set order on all involved processors:

[[processors.rename]]
  order = 1
  [[processors.rename.replace]]
    tag = "path"
    dest = "resource"

[[processors.strings]]
  order = 2
  [[processors.strings.trim_prefix]]
    tag = "resource"
    prefix = "/api/"

Aggregator Plugins

Aggregator plugins produce new metrics after examining metrics over a time period, as the name suggests they are commonly used to produce new aggregates such as mean/max/min metrics. Aggregators operate on metrics after any processors have been applied.

Parameters that can be used with any aggregator plugin:

• alias: Name an instance of a plugin.
• period: The period on which to flush & clear each aggregator. All metrics that are sent with timestamps outside of this period will be ignored by the aggregator.
• delay: The delay before each aggregator is flushed. This is to control how long for aggregators to wait before receiving metrics from input plugins, in the case that aggregators are flushing and inputs are gathering on the same interval.
• grace: The duration when the metrics will still be aggregated by the plugin, even though they're outside of the aggregation period. This is needed in a situation when the agent is expected to receive late metrics and it's acceptable to roll them up into next aggregation period.
• drop_original: If true, the original metric will be dropped by the aggregator and will not get sent to the output plugins.
• name_override: Override the base name of the measurement. (Default is the name of the input).
• name_prefix: Specifies a prefix to attach to the measurement name.
• name_suffix: Specifies a suffix to attach to the measurement name.
• tags: A map of tags to apply to the measurement - behavior varies based on aggregator.

The metric filtering parameters can be used to limit what metrics are handled by the aggregator. Excluded metrics are passed downstream to the next aggregator.

Examples

Collect and emit the min/max of the system load1 metric every 30s, dropping the originals.

[[inputs.system]]
  fieldinclude = ["load1"] # collects system load1 metric.

[[aggregators.minmax]]
  period = "30s"        # send & clear the aggregate every 30s.
  drop_original = true  # drop the original metrics.

[[outputs.file]]
  files = ["stdout"]

Collect and emit the min/max of the swap metrics every 30s, dropping the originals. The aggregator will not be applied to the system load metrics due to the namepass parameter.

[[inputs.swap]]

[[inputs.system]]
  fieldinclude = ["load1"] # collects system load1 metric.

[[aggregators.minmax]]
  period = "30s"        # send & clear the aggregate every 30s.
  drop_original = true  # drop the original metrics.
  namepass = ["swap"]   # only "pass" swap metrics through the aggregator.

[[outputs.file]]
  files = ["stdout"]

Metric Filtering

Metric filtering can be configured per plugin on any input, output, processor, and aggregator plugin. Filters fall under two categories: Selectors and Modifiers.

Selectors

Selector filters include or exclude entire metrics. When a metric is excluded from a Input or an Output plugin, the metric is dropped. If a metric is excluded from a Processor or Aggregator plugin, it is skips the plugin and is sent onwards to the next stage of processing.

• namepass: An array of glob pattern strings. Only metrics whose measurement name matches a pattern in this list are emitted. Additionally, custom list of separators can be specified using namepass_separator. These separators are excluded from wildcard glob pattern matching.

• namedrop: The inverse of namepass. If a match is found the metric is discarded. This is tested on metrics after they have passed the namepass test. Additionally, custom list of separators can be specified using namedrop_separator. These separators are excluded from wildcard glob pattern matching.

• tagpass: A table mapping tag keys to arrays of glob pattern strings. Only metrics that contain a tag key in the table and a tag value matching one of its patterns is emitted. This can either use the explicit table syntax (e.g. a subsection using a [...] header) or inline table syntax (e.g like a JSON table with {...}). Please see the below notes on specifying the table.

• tagdrop: The inverse of tagpass. If a match is found the metric is discarded. This is tested on metrics after they have passed the tagpass test.

NOTE: Due to the way TOML is parsed, when using the explicit table syntax (with [...]) for tagpass and tagdrop parameters, they must be defined at the end of the plugin definition, otherwise subsequent plugin config options will be interpreted as part of the tagpass/tagdrop tables. NOTE: When using the inline table syntax (e.g. {...}) the table must exist in the main plugin definition and not in any sub-table (e.g. [[inputs.win_perf_counters.object]]).

• metricpass: A "Common Expression Language" (CEL) expression with boolean result where true will allow the metric to pass, otherwise the metric is discarded. This filter expression is more general compared to e.g. namepass and also allows for time-based filtering. An introduction to the CEL language can be found here. Further details, such as available functions and expressions, are provided in the language definition as well as in the extension documentation.

NOTE: Expressions that may be valid and compile, but fail at runtime will result in the expression reporting as true. The metrics will pass through as a result. An example is when reading a non-existing field. If this happens, the evaluation is aborted, an error is logged, and the expression is reported as true, so the metric passes.

NOTE: As CEL is an interpreted languguage, this type of filtering is much slower compared to namepass/namedrop and friends. So consider to use the more restricted filter options where possible in case of high-throughput scenarios.

Modifiers

Modifier filters remove tags and fields from a metric. If all fields are removed the metric is removed and as result not passed through to the following processors or any output plugin. Tags and fields are modified before a metric is passed to a processor, aggregator, or output plugin. When used with an input plugin the filter applies after the input runs.

• fieldinclude: An array of glob pattern strings. Only fields whose field key matches a pattern in this list are emitted.

• fieldexclude: The inverse of fieldinclude. Fields with a field key matching one of the patterns will be discarded from the metric. This is tested on metrics after they have passed the fieldinclude test.

• taginclude: An array of glob pattern strings. Only tags with a tag key matching one of the patterns are emitted. In contrast to tagpass, which will pass an entire metric based on its tag, taginclude removes all non matching tags from the metric. Any tag can be filtered including global tags and the agent host tag.

• tagexclude: The inverse of taginclude. Tags with a tag key matching one of the patterns will be discarded from the metric. Any tag can be filtered including global tags and the agent host tag.

Filtering Examples

Using tagpass and tagdrop

[[inputs.cpu]]
  percpu = true
  totalcpu = false
  fieldexclude = ["cpu_time"]
  # Don't collect CPU data for cpu6 & cpu7
  [inputs.cpu.tagdrop]
    cpu = [ "cpu6", "cpu7" ]

[[inputs.disk]]
  [inputs.disk.tagpass]
    # tagpass conditions are OR, not AND.
    # If the (filesystem is ext4 or xfs) OR (the path is /opt or /home)
    # then the metric passes
    fstype = [ "ext4", "xfs" ]
    # Globs can also be used on the tag values
    path = [ "/opt", "/home*" ]

[[inputs.win_perf_counters]]
  [[inputs.win_perf_counters.object]]
    ObjectName = "Network Interface"
    Instances = ["*"]
    Counters = [
      "Bytes Received/sec",
      "Bytes Sent/sec"
    ]
    Measurement = "win_net"
  # Do not send metrics where the Windows interface name (instance) begins with
  # 'isatap' or 'Local'
  [inputs.win_perf_counters.tagdrop]
    instance = ["isatap*", "Local*"]

Using fieldinclude and fieldexclude

# Drop all metrics for guest & steal CPU usage
[[inputs.cpu]]
  percpu = false
  totalcpu = true
  fieldexclude = ["usage_guest", "usage_steal"]

# Only store inode related metrics for disks
[[inputs.disk]]
  fieldinclude = ["inodes*"]

Using namepass and namedrop

# Drop all metrics about containers for kubelet
[[inputs.prometheus]]
  urls = ["http://kube-node-1:4194/metrics"]
  namedrop = ["container_*"]

# Only store rest client related metrics for kubelet
[[inputs.prometheus]]
  urls = ["http://kube-node-1:4194/metrics"]
  namepass = ["rest_client_*"]

Using namepass and namedrop with separators

# Pass all metrics of type 'A.C.B' and drop all others like 'A.C.D.B'
[[inputs.socket_listener]]
  data_format = "graphite"
  templates = ["measurement*"]

  namepass = ["A.*.B"]
  namepass_separator = "."

# Drop all metrics of type 'A.C.B' and pass all others like 'A.C.D.B'
[[inputs.socket_listener]]
  data_format = "graphite"
  templates = ["measurement*"]

  namedrop = ["A.*.B"]
  namedrop_separator = "."

Using taginclude and tagexclude

# Only include the "cpu" tag in the measurements for the cpu plugin.
[[inputs.cpu]]
  percpu = true
  totalcpu = true
  taginclude = ["cpu"]

# Exclude the "fstype" tag from the measurements for the disk plugin.
[[inputs.disk]]
  tagexclude = ["fstype"]

Metrics can be routed to different outputs using the metric name and tags

[[outputs.influxdb]]
  urls = [ "http://localhost:8086" ]
  database = "telegraf"
  # Drop all measurements that start with "aerospike"
  namedrop = ["aerospike*"]

[[outputs.influxdb]]
  urls = [ "http://localhost:8086" ]
  database = "telegraf-aerospike-data"
  # Only accept aerospike data:
  namepass = ["aerospike*"]

[[outputs.influxdb]]
  urls = [ "http://localhost:8086" ]
  database = "telegraf-cpu0-data"
  # Only store measurements where the tag "cpu" matches the value "cpu0"
  [outputs.influxdb.tagpass]
    cpu = ["cpu0"]

Routing metrics to different outputs based on the input

Metrics are tagged with influxdb_database in the input, which is then used to select the output. The tag is removed in the outputs before writing with tagexclude.

[[outputs.influxdb]]
  urls = ["http://influxdb.example.com"]
  database = "db_default"
  [outputs.influxdb.tagdrop]
    influxdb_database = ["*"]

[[outputs.influxdb]]
  urls = ["http://influxdb.example.com"]
  database = "db_other"
  tagexclude = ["influxdb_database"]
  [outputs.influxdb.tagpass]
    influxdb_database = ["other"]

[[inputs.disk]]
  [inputs.disk.tags]
    influxdb_database = "other"

Transport Layer Security (TLS)

Reference the detailed TLS documentation.